The Arbiter is one of the most popular characters in the Halo series because of the role he played in Halo 2 when he turned on the Covenant and later became an ally of Master Chief in Halo 3. Since those days, he has not done much in the story aside from a quick appearance in Halo 5: Guardians. That being said, there is a neat little Easter egg plushie you can find of him in Halo Infinite. Here is where.
To find the Arbiter plushie, you will need to go to the landmass in the most northwest of the map, right next to Fort Tremonius. The best way to get over there that we found was via a Banshee, but you may be able to find another method. When you have the means, travel to this location in the screenshot below.
Once you have reached this area, look for this cave on the side of the mountain. Either Grappleshot or jump over to it from the path to the left and enter.
On the left side of the cavern you just entered will be a plush Arbiter with its arms stretched out.
As of this writing, we have not found any other kind of Easter egg functionality with this plushie; it just seems to be an environmental nod to the character.